Adaptive agc system

ABSTRACT

Acoustic information is applied to a transducer and the electrical signal from the transducer is supplied to a modulator and transmitted if the signal both exceeds a predetermined level for a specified period of time and increases during this time above a specified rate. This is attained by applying the electrical signal to an AGC difference circuit with a feedback control so that the AGC difference circuit provides a constant output that is not transmitted so long as the input signal does not increase above a predetermined rate. If however the signal increases above the predetermined rate a field effect transistor difference amplifier senses the increased rate and fires a Schmitt trigger whose output applied to an integrator circuit for a specified period of time actuates a control gate enabling battery power to be applied to a transmitter for transmission of a modulated signal carrying the acoustic information.

9 Elite States Patent 1 m1 3,714,622 Wilhelmsen 1 Jan. 30, 1973 s41ADAPTIVE AGC SYSTEM 2,675,469 4/1954 Harkeretal. .l; ..328/l28 [75] In tCarl R. wilhelmsen, Huntington 3,164,787 1/1965 Fontame ..328/l28Station Primary ExaminerBenjamin A. Borchelt [73] Assignee: The UnitedStates of America as AssisfamExaminerfl'l-A-Bil'miel represented by thesecretary f h Att0rneyR. S. Sclascia and Henry Hansen Navy [57] ABSTRACT[22] Filed: Dec. 12, 1969 Acoustic information is appliedto a transducerand PP 884,419 the electrical signal from the transducer 'is supplied toa modulator and transmitted if the signal both exceeds a predeterminedlevel for a specified period of time 52 US. Cl. .340 16 307 263, 3251l3, i 1 325/152 325/1,87 3254341 324402 and increases during this timeabove a specified rate. electrical Signal t0 an [51] Int Cl 6 13,16 AGCdifference circuit with a feedback control so that [58] Fieid 258 theAGC difference circuit provides a constant output 325/62 341 3O7I263that is not transmitted so long as the input signal does 79/1 notincrease above a predetermined rate. If however the signal increasesabove the predetermined rate a R f C1 d field effect transistordifference amplifier senses the [56] e erences e increased rate andfires a Schmitt trigger'whose output UNITED STATES PATENTS applied to anintegrator circuit for a specified period of time actuates a controlgate enabling battery power 3,564,493 2/l97l Hicklin ..340/15 to beapplied to a transmitter for transmission of a 2,692,334 0/1954 Blumlam-328/128 modulated signal carrying the acoustic information. 3,276,0069/1966 Hansen ..340/26l j 3,552,520 1/1971 Naubereit ..340/l6 C 8Claims, 2 Drawing Figures 24 29 25 23 32 LIMITER MODULATOR XllMTTER 10 H21 i3 14 I51 i6 y 2o-\ 1 '3 i Z JS I INTEGRATOR ggg' -flgg mreenaron inL RM 06 in ZZN BATTERY ms Q5 4 oz RS l FROM I! 5. CW m ,3

as H

ADAPTIVE AGC SYSTEM STATEMENT OF GOVERNMENT INTEREST The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates generally to a radiotransmission system in which acoustic information is applied to atransducer and the transducers output electrical signal is amplified andfed to a modulator for modulating a radio frequency signal fortransmission purposes. More particularly, the invention pertains to asystem in which transmission occurs only if the input acoustic signal isof sufficient magnitude and increases above a specific rate for apredetermined period of time. Such a system is particularly useful indetecting the movement of motor vehicles.

The transmitter is energized by a d.c. power supply with limited usefullife. It therefore becomes imperative that the power supply not be usedat times when the received signal is not of sufficient importance. Inorder to accomplish this result the system itself has built into it ameans of determining useful information so that only this usefulinformation is transmitted to a distant point. At other times in orderto prolong the useful life of the system it is necessary that the powersupply is not m use.

SUMMARY OF THE INVENTION Accordingly, it is a general purpose of thepresent invention to provide a system that distinguishes between aconstant sound level and a rising sound level.

This is accomplished by a feedback from a Millertype integrator to anAGC system so that signals whose rate of increase do not exceed apredetermined rate provide a constant output. If this threshold ofrate-increase is exceeded for a predetermined period of time in a signalof sufficient magnitude this increased level is detected and a controlswitch applies battery power to a transmitter so that this desiredsignal is transmitted to a distant receiving station.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of'a systemaccording to the invention; and

FIG. 2 is a schematic circuit diagram of an AGC difboth amplifiers l3and 14. An envelope detector 17 receives the output of amplifier l6 andin a manner well known in the art provides a signal that is indicativeference amplifier and a Miller-type integrator as applied to the systemof FIG. 1.

Referring to FIG. 1, a microphone 10 is adapted to receive an acousticsignal and transmit an electrical signal representativeof the receivedacoustic signal to a preamplifier 11. The signal from the preamplifier11 is applied to one of two inputs of an AGC difference amplifier 12.The output of the AGC difference amplifier 12 is respectively amplifiedthrough identical amplifiers 13 and 14 connected in series. A bufferamplifier 15 is interposed after amplifier 14 to isolate the load fromthe remainder of the circuit. The output of the amplifier 15 is appliedto another amplifier 16 identical to of the peaks of the signal appliedthereto. The output of signal to the AGC difference amplifier 12 isexceeded.

In the event the input signal does exceed the predetermined rate theoutput of the AGC difference amplifier 12 is increased and this increaseis sensed by a differential amplifier 19 connected to the output ofMiller-type integrator 18. Amplifier 19 on sensing the increase inamplitude of the signal at the integrator 18 provides an output signalthat fires a conventional Schmitt trigger 20. The trigger 20 on beingactuated applies a constant level signal to an integrator 31. If thetrigger 20 remains fired for a predetermined period of time the outputsignal of integrator 31 rises to a sufficient value to actuate a controlgate 21. Control gate 21 on being actuated connects a battery 22 to atransmitter 23 so that the transmitter 23 sends an applied signal bymeans of an antenna 32 to a distant receiver (not shown).

The amplifier 14 in addition to supplying its output signal to amplifier15 also supplies its output signal to an amplifier 24 that in turnprovides a signal to the input of a limiter 29. The limiter 29 providesan audio signal to a modulator 25 below the threshold amplitude thatwould cause overmodulation. Modulation of an r.f. signal by the audiosignal containing the acoustic information takes place in the modulator25 and this modulated signal is applied to the transmitter 23 which isconnected to the antenna 32. Transmission occurs only on the activationof control gate 21 by means previously described.

Referring now to FIG. 2 there is shown a schematic diagram of the AGCdifference amplifier 12 and the Miller-type integrator 18 in itsfeedback circuit.

The preamplifier l1 is connected to a coupling capacitor C7 that has itsother terminal connected to a voltage divider comprised, in one legconnected to a d.c. supply +V, of aidiode CR3 and a resistor R6 and, in

the other leg connected to ground, a resistor R7. Theprising a resistorR13 in one leg connected to the +V, and a resistor R8 together with anMOS field effectt'ransistor Q15 inthe other leg connected to ground.Transistor Q6 has its base connected to a dividing circuit comprising aresistor R15 in one leg' connected to the +V and a resistor R12 in theother leg connected to ground. A resistor R11 is connected between thecollector of transistor 06 and ground. The collector of transistor O6 isalso coupled as the output of amplifier 12 to the amplifier 13 through acoupling capacitor C10.

One terminal of a resistor R48 of the integrator 18 is connected todetector 17. The other terminal of resistor R48 is connected to the gateof transistor Q15 and parallel capacitors C58, C59 and C33. The otherterminals on the capacitors are tied together and connected to the drainof transistor Q15. The transistor Q15 has its sources tied together andgrounded. Resistor R48 also has its two terminals connected to therespective inputs of difference amplifier 19 so that amplifier 19 maydetect a voltage drop across resistor R48 above a predetermined level.

The operation of the AGC difference amplifier 12 with its associatedfeedback from Miller-type integrator 18 will now be explained.

A signal from the preamplifier 11 is applied to the base of transistorQ2. In response to the applied signal the collector of transistor Q2supplies a current signal to the emitters of transistors Q5 and Q6 thatis proportional to the signal applied to the base of transistor Q2. Thiscurrent divides with a fraction of it passing to the grounded collectorof transistor 05 and the remainder passing to the collector oftransistor Q6 as an output signal to be supplied to amplifier 13. Thissignal in modified form is received by integrator 18. In integrator 18the signal is applied to the gate of transistor Q15. A rise in the levelof the signal applied to the gate of transistor Q will make Q15 moreconductive therefore causing more current to flow from +V through theseries combination ofR13, R8 and 015 to ground. This will in turn lowerthe voltage applied to the base of transistor Q5 so that the transistorwill pass more current from transistor O2 to ground if the amplitude ofthe signal is rising in order to maintain a constant current throughtransistor 06. Conversely if the current signal from transistor 02 isfailing the feedback signal applied to the base of transistor-Q5 lowersthe current through transistor Q5 maintaining a constant current throughtransistor 06.

When the current signal from transistor Q2 increases above apredetermined rate the integrator 18 does not respond quickly enough tohave a sufficient change in the signal applied to the base of transistorOS that would shunt the increased current through transistor Q5. As aresult the current through transistor O6 increases and if the currentsignal is of sufficient magnitude this increased signal provides asufficient voltage drop across resistor R48 to operate amplifier 19.This operation of amplifier 19 results in transmitter 23 being turned onas previously described.

It can therefore be seen that the system provides for an output signalfrom transmitter 23 only when the input signal exceeds a predeterminedlevel and is of a rising magnitude above a predetermined rate. ln thismanner a self-contained, battery-supplied unit is able to operate over asufficiently long period of time. The alternative of providing aconstant transmission of the signal applied to the microphone wouldquickly use up the battery power and render the system of far lessvalue.

Obviously many modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

l. A detector system comprising:

signal generating means for generating an electrical signal; and

detecting means having a difference amplifier for receiving both saidelectrical signal and a feedback signal and providing an output signal,envelope detector means for receiving said difference amplifier outputsignal and providing an output signal indicative of the peaks of thereceived difference amplifier output signal, and integrator means forreceiving said envelope detector means output signal and providing saidfeedback signal having a rate of increase within a predetermined limit,and providing an output signal proportional to the dif ference in therates of change of said received envelope detector means output signaland said feedback signal, said detecting means providing an outputsignal only if the rate of increase in amplitude of said electricalsignal exceeds a predetermined rate.

2. A detector system according to claim 1 wherein said integrator meansfurther comprises:

resistor means connected at one end for receiving said envelope detectormeans output signal;

capacitor means having one side connected to the other end of saidresistor means; and

field effect transistor means having a gate connected to the junction ofsaid resistor means and capacitor means, a source connected to ground,and a drain connected to said one side of said capacitor means forproviding said feedback signal.

3. A detector system according to claim 2 wherein said signal generatingmeans further comprises:

a microphone for detecting an acoustic signal and providing saidelectrical signal of a frequency and amplitude indicative of theacoustic signal detected.

4. A radio transmission system comprising:

transducer means for detecting sound and providing a first signalindicative of the amplitude and frequency of the sound;

circuit means for receiving said first signal and providing a secondsignal of constant rate-increasing amplitude when the rate of increaseof the amplitude of said first signal exceeds a predetermined rate andproviding a third signal indicative of the frequency of said firstsignal and the amount the rate of increase of amplitude of said firstsignal exceeds a predetermined rate of increase;

control means for receiving said second signal and providing power at apredetermined level of said received signal; and

transmitter means for receiving said third signal and said power andproviding an r.f. output signal indicative of the sound.

5. A radio transmission system according to claim 4 wherein said circuitmeans further comprises:

a difference amplifier for receiving said first signal and a feedbacksignal and providing said third signal;

detector means for receiving said third signal and providing an outputsignal indicative of the peaks of the received signal;

first integrator means for receiving said detector means output signaland providing said feedback signal having a rate of increase within apredetermined limit, and an output signal proportional to the differencein the rates of change of said received signal and said feedback signal;

a Schmitt trigger for receiving said first integrator means outputsignal and providing an output when the received signal exceeds apredetermined level; and

second integrator means for receiving and integrating said triggeroutput and providing said second signal.

6. A radio transmission system according to claim 5 wherein saidtransmitter means further comprises:

limiter means for receiving said third signal and providing an outputsignal indicative of the frequency and predetermined maximum amplitudeof the received signal;

modulator means for receiving the limiter means output signal andproviding an r.f. output signal modulated in accordance with thereceived signal; and

antenna means for receiving and transmitting said modulator means outputsignal.

7. A radio transmission system according to claim 6 wherein said controlmeans further comprises:

an electrical power source; and

switching means for receiving said second signal and the output of saidsource for providing said power;

8. A measuring system comprising:

generating means for providing a gain controlled variable d.c. signal;

resistor means connected at one end for receiving said variable d.c.signal;

capacitor means having one side connected to the other end of saidresistor means;

a field effect transistor having a gate connected to the junction ofsaid resistor means and capacitor means for receiving said d.c. signal,a source connected to ground, and a drain connected to the other side ofsaid capacitor means;

first connection means connected from the junction of said drain andcapacitor means to said generating means for controlling said variabled.c. signal;

second connection means connected to both ends of said resistor meansfor providing an output signal indicative of a voltage drop across saidresistor means.

1. A detector system comprising: signal generating means for generating an electrical signal; and detecting means having a difference amplifier for receiving both said electrical signal and a feedback signal and providing an output signal, envelope detector means for receiving said difference amplifier output signal and providing an output signal indicative of the peaks of the received difference amplifier output signal, and integrator means for receiving said envelope detector meAns output signal and providing said feedback signal having a rate of increase within a predetermined limit, and providing an output signal proportional to the difference in the rates of change of said received envelope detector means output signal and said feedback signal, said detecting means providing an output signal only if the rate of increase in amplitude of said electrical signal exceeds a predetermined rate.
 1. A detector system comprising: signal generating means for generating an electrical signal; and detecting means having a difference amplifier for receiving both said electrical signal and a feedback signal and providing an output signal, envelope detector means for receiving said difference amplifier output signal and providing an output signal indicative of the peaks of the received difference amplifier output signal, and integrator means for receiving said envelope detector meAns output signal and providing said feedback signal having a rate of increase within a predetermined limit, and providing an output signal proportional to the difference in the rates of change of said received envelope detector means output signal and said feedback signal, said detecting means providing an output signal only if the rate of increase in amplitude of said electrical signal exceeds a predetermined rate.
 2. A detector system according to claim 1 wherein said integrator means further comprises: resistor means connected at one end for receiving said envelope detector means output signal; capacitor means having one side connected to the other end of said resistor means; and field effect transistor means having a gate connected to the junction of said resistor means and capacitor means, a source connected to ground, and a drain connected to said one side of said capacitor means for providing said feedback signal.
 3. A detector system according to claim 2 wherein said signal generating means further comprises: a microphone for detecting an acoustic signal and providing said electrical signal of a frequency and amplitude indicative of the acoustic signal detected.
 4. A radio transmission system comprising: transducer means for detecting sound and providing a first signal indicative of the amplitude and frequency of the sound; circuit means for receiving said first signal and providing a second signal of constant rate-increasing amplitude when the rate of increase of the amplitude of said first signal exceeds a predetermined rate and providing a third signal indicative of the frequency of said first signal and the amount the rate of increase of amplitude of said first signal exceeds a predetermined rate of increase; control means for receiving said second signal and providing power at a predetermined level of said received signal; and transmitter means for receiving said third signal and said power and providing an r.f. output signal indicative of the sound.
 5. A radio transmission system according to claim 4 wherein said circuit means further comprises: a difference amplifier for receiving said first signal and a feedback signal and providing said third signal; detector means for receiving said third signal and providing an output signal indicative of the peaks of the received signal; first integrator means for receiving said detector means output signal and providing said feedback signal having a rate of increase within a predetermined limit, and an output signal proportional to the difference in the rates of change of said received signal and said feedback signal; a Schmitt trigger for receiving said first integrator means output signal and providing an output when the received signal exceeds a predetermined level; and second integrator means for receiving and integrating said trigger output and providing said second signal.
 6. A radio transmission system according to claim 5 wherein said transmitter means further comprises: limiter means for receiving said third signal and providing an output signal indicative of the frequency and predetermined maximum amplitude of the received signal; modulator means for receiving the limiter means output signal and providing an r.f. output signal modulated in accordance with the received signal; and antenna means for receiving and transmitting said modulator means output signal.
 7. A radio transmission system according to claim 6 wherein said control means further comprises: an electrical power source; and switching means for receiving said second signal and the output of said source for providing said power. 